This invention relates to an apparatus for deciding an excessive approach of an automotive vehicle to an object in front of the vehicle.
In an article entitled "Radar For Car Crash Prevention", Nissan Technical Journal, No. 18, 1982, there is described a conventional excessive approach decision apparatus which utilizes a safety distance Rs (in meters) calculated as ##EQU1## where Vr (in meters per seconds) is the speed of the vehicle with respect to the one in front, Va (in meters per seconds) is the speed of the vehicle on which the radar is installed, Td (in seconds) is the driver's response time, K (in meters) is the distance between the vehicles when the application of braking to the vehicle is completed, and .alpha. is the deceleration (g). Equation (1) represents the condition where the vehicle can come to a safety stop with a distance K spaced away from the vehicle in front when both of the vehicles are decelerated at an acceleration of .alpha..
FIG. 10 is a graph of safety distance Rs versus vehicle speed Va. The broken curve indicates the safety distance Rs with respect to the vehicle speed Va when Vr=Va, that is, the vehicle in front is at rest. In order to prevent a pile-up, i t is required to retain the safety distance Rs indicated by the broken curve. Therefore, it is the conventional practice to produce an alarm when the distance of the vehicle away from the vehicle in front is equal to or less than the safety distance calculated from Equation (1).
Since such a conventional excessive approach decision apparatus decides an excessive approach based upon the distance Rs which permits the vehicle to come to a stop with no collision with the vehicle held at rest in front of the vehicle, however, it is very difficult, if not impossible to produce the alarm in agreement with the driver's sense for an excessive approach without annoying the driver.